1. Field of the Invention
The present invention relates to a magnetic head for recording by applying a magnetic field to a recording medium, and particularly to a magnetic head with uniform quality comprising a magnetic layer which can be precisely formed with a decreased amount of processing. The present invention also relates to a method for manufacturing the magnetic head.
2. Description of the Related Art
Each of Japanese Unexamined Patent Application Publication Nos. 11-232609 and 7-272211 discloses a method for manufacturing a magnetic head. As shown in FIG. 2 of Japanese Unexamined Patent Application Publication No. 11-232609, the method for manufacturing a magnetic head comprises forming an alumina film for forming a gap so that it projects from a substrate, forming a permalloy film to cover the alumina film (FIG. 2(a)), forming a SiO2 film over the permalloy film (FIG. 2(b)), and polishing the alumina film together with the SiO2 and permalloy films using a horizontal plane formed in the SiO2 film as a stopper for stopping the polishing (FIG. 2(c)).
FIG. 2(b) of Japanese Unexamined Patent Application Publication No. 11-232609 shows a state in which the upper surface of the permalloy film covering the alumina film depends on the shape of the alumina film.
However, when the permalloy film is actually formed over the alumina film, the permalloy film is formed in such a shape as shown in FIG. 20 based on the shape of the alumina film, unlike the shape shown in FIG. 2(b) of Japanese Unexamined Patent Application Publication No. 11-232609.
FIG. 20 is a drawing showing an actual state rewritten from the state shown in FIG. 2(b) of Japanese Unexamined Patent Application Publication No. 11-232609. In FIG. 20, reference numeral 1 denotes a substrate; reference numeral 2, an alumina film; reference numeral 3, a permalloy film; and reference numeral 4, a SiO2 film.
As shown in FIG. 20, the upper surface 3a of the permalloy film 3 formed over the alumina film 2 on the substrate 1 includes first, second, and third concave portions 3b, 3c, and 3d formed above the left edge 2a, the right edge 2b, and the top edge 2c, respectively, of the alumina film 2. This is because when the permalloy film 3 is formed over the alumina film 2, the permalloy film 3 is grown on the horizontal plane (substantially parallel to the X-Y direction shown in the drawing) 2e of the alumina film 2 in the direction (the Z direction shown in the drawing) substantially perpendicular to the horizontal plane 2e, and thus the growth rate of the permalloy film 3 in the Z direction is high. However, on the vertical plane (substantial parallel to the Z direction) 2f of the alumina film 2, the permalloy film 3 is easily grown in the direction (i.e., the X direction shown in the drawing) perpendicular to the vertical plane, and thus the growth rate of the permalloy film 3 on the vertical plane 2f is lower than that on the horizontal plane 2e in the Z direction. The growth rate of the permalloy film 3 on the horizontal plane 2e is different from that on the vertical plane 2f in the Z direction shown in the drawing. Therefore, the thickness of the permalloy film 3 on the horizontal plane 2e becomes different from that on the vertical plane 2f in the Z direction shown in the drawing.
Japanese Unexamined Patent Application Publication No. 7-272211 also discloses a process for manufacturing a magnetic head on the basis of the same idea as that of the invention disclosed in Japanese Unexamined Patent Application Publication No. 11-232609. As shown in FIG. 1 of Japanese Unexamined Patent Application Publication No. 7-272211, the method for manufacturing a magnetic head comprises forming a magnetic core on a substrate with a first insulation layer provided therebetween, forming a second insulation layer to cover the sides and the top of the magnetic core, forming a hard metal layer on the second insulation layer to form a wafer (FIG. 1(a)), and polishing the magnetic core together with the hard metal film and the second insulation layer (FIGS. 1(b) and (c)) using a horizontal plane formed on the hard metal film as a polishing stopper for stopping the polishing (FIG. 1(d)).
FIG. 1(a) of Japanese Unexamined Patent Application Publication No. 7-272211 shows a state in which the upper surface of the second insulation layer covering the magnetic core depends on the shape of the magnetic core.
However, when the second insulation layer is actually formed over the magnetic core, the second insulation layer is formed in such a shape as shown in FIG. 21 on the basis of the shape of the magnetic core.
FIG. 21 is a drawing showing an actual state rewritten from the state shown in FIG. 1(a) of Japanese Unexamined Patent Application Publication No. 7-272211. In FIG. 21, reference numeral 11 denotes a substrate; reference numeral 12, a first insulation layer; reference numeral 13, a magnetic core; reference numeral 14, a second insulation layer; and reference numeral 15, a hard meal film.
As shown in FIG. 21, the upper surface 14a of the second insulation layer 14 formed over the magnetic core 13 includes first and second concave portions 14a and 14c formed on the sides of the left side 13a and the right side 13b, respectively, of the magnetic core 13. This is because when the second insulation layer 14 is formed over the magnetic core 13, the second insulation layer 14 is grown on the horizontal plane 13c of the magnetic core 13, which is substantially parallel to the X-Y direction shown in the drawing, in the direction (the Z direction shown in the drawing) substantially perpendicular to the horizontal plane 13c, and thus the growth rate of the second insulation layer 14 in the Z direction is high. However, on both sides 13a and 13b perpendicular to the horizontal plane 13c, the second insulation layer 14 is easily grown on both sides 13a and 13b in the X direction shown in the drawing, and thus the growth rate of the second insulation layer 14 on both sides 13a and 13b is lower than that on the horizontal plane 13c in the Z direction. The growth rate of the second insulation layer 14 on the horizontal plane 13c is different from that on both sides 13a and 13b in the Z direction shown in the drawing. Therefore, the thickness of the second insulation layer 14 on the horizontal plane 13c becomes different from that on both sides 13a and 13b in the Z direction shown in the drawing.
When a magnetic layer of a magnetic head is produced based on the methods for manufacturing a magnetic head disclosed in the above-described documents, the magnetic layer can be produced by the method shown in FIGS. 22 to 26.
First, as shown in FIG. 22, a seed layer 22 is formed on a substrate 21. Next, as shown in FIG. 23, a magnetic layer 23 is formed on the seed layer 22 by a resist process (using resist R shown in the drawing), and then the resist R is removed. Then, as shown in FIG. 24, a third material layer 24 is formed to cover the magnetic layer 23. As shown in FIG. 25, a second material layer 25 is formed to cover the third material layer 24. Then, the third material layer 24 and the magnetic layer 23 are polished along line D-D shown in FIG. 25 together with the second material layer 25 to form the magnetic layer 23 for a magnetic head in the state shown in FIG. 26. In the state shown in FIG. 25, like in the states shown in FIG. 20 and 21 rewritten from the states shown in FIG. 2(b) and FIG. 1(a) of Japanese Unexamined Patent Application Publication Nos. 11-232609 and 7-272211, respectively, the second material layer 25 has concave portions 25a formed on both sides of the magnetic layer 23. This is because like in the manufacturing methods disclosed in Japanese Unexamined Patent Application Publication Nos. 11-232609 and 7-272211, the growth rate of the second material layer 25 on the horizontal plane 24a (parallel to the X-Y plane shown in FIG. 25) is different from that on the vertical plane 24b (parallel to the Z direction shown in FIG. 25) in the Z direction. In this case, the growth rate on the horizontal planes 24a is higher than that on the vertical plane 24b. Namely, the second material layer 25 grown on the horizontal plane 24a joins the second material layer 25 grown on the vertical planes 24b above the corners 26 formed at the respective boundaries between the horizontal plane 24a and the vertical planes 24b, thereby forming the larger concave portions 25a above the corners 26.
When polishing is performed for forming the magnetic layer 23 for a vertical magnetic recording magnetic head in the step shown in FIG. 25, differences between the polishing rates of the second material layer 25, the third material layer 24, and the magnetic layer 23 cause a problem in which a portion concaving in the direction opposite to the Z direction, i.e., dishing, occurs in the upper surface 23a of the magnetic layer 23 after polishing as shown in FIG. 27, or a portion projecting in the Z direction occurs on the upper surface 23 of the magnetic layer 23 as shown in FIG. 28. The problem is due to the fact that the materials are polished in different degrees because of differences between the CMP processing rates of the second material layer 25, the third material layer 24, and the magnetic layer 23.
When the dishing or the projecting portion occurs on the upper surface 23a of the magnetic layer 23, a recording signal is recorded in a distorted form on a recording medium to fail to perform accurate recording, thereby causing the problem of generating noise, i.e., smile, during reproduction of the recording signal. Therefore, the upper surface 23a of the magnetic layer 23 must be formed as a planarized surface.
When a magnetic head is manufactured by any one of the conventional methods for manufacturing a magnetic head shown in FIGS. 20 and 21, and 22 to 26, the concave portions 3b, 3c, and 3d, 14b and 14c, or 25a remain in the polished surface after polishing unless polishing is performed to a portion below the lower ends of the concave portions 3b, 3c, and 3d shown in FIG. 20, the lower ends of the concave portions 14b and 14c shown in FIG. 21, or the lower ends 25b of the concave portions 25a shown in FIG. 25 in the polishing step. As a result, the polished surface cannot be formed as a planarized surface. Therefore, in order that the polished surface can be formed as a planarized surface, polishing must be performed to a portion below the lower ends of the concave portions 3b, 3c, and 3d, 14b and 14c, or 25a in the polishing step, and thus the polishing amount must be increased.
Also, in the CMP (polishing) performed in the method for manufacturing a magnetic head shown in FIG. 25, when the dishing or the projecting portion occurs on the upper surface 23a of the magnetic layer 23, a planarized surface cannot be formed unless the polishing amount of the magnetic layer 23 is increased by an amount corresponding to the concave portion occurring due to dishing or the projecting portion. Therefore, the polishing amount must be increased.
However, polishing error and variations in the polishing amount are increased as the polishing mount is increased, and there is thus limitation in precise manufacture of a magnetic head having uniform quality.
Also, when the polishing amount is increased, each of the members must be formed in a larger thickness in expectation of an increase in the polishing amount, thereby increasing the manufacturing time and cost.